Image pickup apparatus, method of controlling image pickup apparatus, and non-transitory computer-readable storage medium

ABSTRACT

An image pickup apparatus includes an image pickup element configured to photoelectrically convert an optical image, and a controller configured to control a drive of a focus lens based on a signal outputted from the image pickup element and control a frame rate to drive the image pickup element, and the controller is configured to detect an in-focus position based on a signal outputted from the image pickup element which is driven at a first frame rate, and to switch the frame rate of the image pickup element to a second frame rate lower than the first frame rate while performing a first operation to drive the focus lens to the in-focus position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 14/262,184,filed Apr. 25, 2014 the entire disclosure of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image pickup apparatus whichperforms focus detection by a contrast method.

2. Description of the Related Art

Conventionally, image pickup apparatuses which have a live view functionand perform auto focus detection (AF control) by a contrast method havebeen known. The AF control by the contrast method requires calculatingcontrast evaluation values while changing a focus position of a focuslens to determine a position at which a contrast evaluation valuereaches a peak.

In order to increase in speed of the AF control by the contrast method,a configuration may be adopted in which a frame rate during the focusdetection is switched to a high-speed frame rate to reduce a samplingcycle of a contrast evaluation value, thereby a focus lens is driven athigher speed for detection of the contrast evaluation value. In thisconfiguration, a frame rate during the AF control is set higher thanthat set during a normal state, taking a processing load of a system(the image pickup system), a battery remaining time depending onconsumption current, and other factors into consideration. JapanesePatent Laid-Open No. (“JP”) 2013-25107 discloses an image pickupapparatus which performs the AF control with a frame rate being switchedto 120 fps by pressing a release button half way when the frame rateduring live view is 60 fps and sets the switched frame rate to theoriginal frame rate of 60 fps after completion of the AF control.

In order for an image pickup apparatus to start a shooting, it istypically required that the AF control be completed to cause a focuslens to be located at an optimum focus position and photometryprocessing to determine an exposure during the shooting be completed.Such photometry processing is required to be performed after an in-focusframe (a focus frame) is fixed in a multi-point AF or other mode inwhich a focus detection frame (an AF frame) to be used for focusing isnot fixed.

However, the image pickup apparatus disclosed in JP 2013-25107 switchesa frame rate from 120 fps to 60 fps after the AF control to set a normallive-view state when the release button is pressed all the way at onceduring the AF control. The image pickup apparatus then permits ashooting after performing photometry to determine an exposure set forthe shooting. Since a frame rate switching typically requires apredetermined time, a focus state may still not be optimized from theviewpoint of a release time lag even when the AF control is performed athigher speed.

On the other hand, in a configuration designed to keep, for apredetermined time during the AF control, a state in which an originalframe rate is switched to a high-speed frame rate, a battery life isshorter due to increase in consumption current and a live-view operationduration is shorter due to rise in temperature, compared with aconfiguration in which a frame rate is returned to a normal frame rateimmediately after the AF control.

In addition, the image pickup apparatus disclosed in JP 2013-25107 isconfigured to start the focus detection by the contrast method afterchanging a frame rate from a low frame rate to a high frame rate. Thismakes it impossible to start the focus detection until completion of theframe rate change, which in turn requires a great deal of time for thefocus detection.

SUMMARY OF THE INVENTION

The present invention provides an image pickup apparatus capable ofperforming high-speed shooting with suppressed consumption current andtemperature rise, a method of controlling the image pickup apparatus,and a non-transitory computer-readable storage medium. The presentinvention also provides an image pickup apparatus capable of displayinga desired live view while performing high-speed focus detection, amethod of controlling the image pickup apparatus, and a non-transitorycomputer-readable storage medium.

An image pickup apparatus as one aspect of the present inventionincludes an image pickup element configured to photoelectrically convertan optical image, and controller configured to control a drive of afocus lens based on a signal outputted from the image pickup element andcontrol a frame rate to drive the image pickup element, and thecontroller is configured to detect an in-focus position based on asignal outputted from the image pickup element which is driven at afirst frame rate and switch the frame rate of the image pickup elementto a second frame rate lower than the first frame rate while performinga first operation to drive the focus lens to the in-focus position.

A method of controlling an image pickup apparatus as another aspect ofthe present invention includes the steps of converting photoelectricallyan optical image in an image pickup element, detecting an in-focusposition based on a signal outputted from the image pickup elementdriven at a first frame rate, performing a first operation to drive afocus lens to the in-focus position, and switching a frame rate of theimage pickup element to a second frame rate lower than the first framerate while performing the first operation.

A non-transitory computer-readable storage medium as another aspect ofthe present invention stores a program which causes a computer toexecute a process that includes the steps of convertingphotoelectrically an optical image in an image pickup element, detectingan in-focus position based on a signal outputted from the image pickupelement driven at a first frame rate, performing a first operation todrive a focus lens to the in-focus position, and switching a frame rateof the image pickup element to a second frame rate lower than the firstframe rate while performing the first operation.

Further features and aspects of the present invention will becomeapparent from the following description of exemplary embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the configuration of an imagepickup system in first and second embodiments.

FIG. 2 is an explanatory diagram of an AF control in the first andsecond embodiments

FIG. 3 is an explanatory diagram of operation timings of the AF controland the photometry processing in the first embodiment.

FIG. 4 is a flowchart of the AF control and the photometry processing inthe first embodiment.

FIG. 5 is an explanatory diagram of operation timings of the AF controland the photometry processing in the second embodiment.

FIG. 6 is a flowchart of the AF control and the photometry processing inthe second embodiment.

FIG. 7 is a block diagram illustrating the configuration of an imagepickup apparatus (an image pickup system) in a third embodiment.

FIG. 8 is a flowchart of a method of controlling the image pickupapparatus (a focus detection method) in the third embodiment.

FIGS. 9A and 9B are a plan view and a cross-sectional view,respectively, of an image pickup pixel of an image pickup element in thethird embodiment and a fourth embodiment.

FIGS. 10A and 10B are a plan view and a cross-sectional view,respectively, of a focus detection pixel of the image pickup element inthe third and fourth embodiments.

FIGS. 11A and 11B are a plan view and a sectional view, respectively, ofa focus detection pixel of the image pickup element in the third andfourth embodiments.

FIG. 12 is a diagram conceptually explaining a situation in which apupil of the image pickup element in the third and fourth embodiments isdivided.

FIG. 13 is a block diagram illustrating the configuration of an imagepickup apparatus (an image pickup system) in the fourth embodiment.

FIG. 14 is a flowchart of a method of controlling the image pickupapparatus (a focus detection method) in the fourth embodiment.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described belowwith reference to the accompanied drawings. In each of the drawings, thesame elements will be denoted by the same reference numerals and theduplicate descriptions thereof will be omitted.

First Embodiment

First of all, referring to FIG. 1, the schematic configuration of animage pickup system (a camera system) in this embodiment will bedescribed. FIG. 1 is a block diagram illustrating the configuration ofthe image pickup system. In FIG. 1, reference numeral 100 denotes animage pickup apparatus (a camera or an image pickup apparatus body), andreference numeral 200 denotes a lens unit (a lens apparatus or aninterchangeable lens). As described above, the image pickup system ofthis embodiment includes the image pickup apparatus 100 and the lensunit 200 removably mounted on the image pickup apparatus 100. Thisembodiment is applicable also to an image pickup apparatus (an imagepickup system) constituted by the lens unit 200 and the image pickupapparatus body which are integrated with each other.

The configuration and the operation of the image pickup apparatus 100will be now described. A camera microcomputer 101 (a controller or aCCPU) is a system control circuit configured to control each element ofthe image pickup apparatus 100. The camera microcomputer 101 isconfigured to perform various controls of the image pickup system andvarious condition determinations as well. An image pickup element 102,which is constituted by a CCD, CMOS, or other sensor, includes aninfrared cut filter, a low-pass filter, and the like. An object image(an optical image) is formed via a lens 202 (or a plurality of lenses)in the lens unit 200, and the object image formed via the lens 202 isimaged on the image pickup element 102. The image pickup element 102photoelectrically converts the object image.

A shutter 103 closes during shot image reading to shield the imagepickup element 102 from light and opens during live view or shooting toguide a ray to the image pickup element 102. The “live view” is afunction which enables to check a shot image by sequentially outputtingimage signals continuously read from the image pickup element 102 on adisplay 113, such as a liquid crystal display, placed on the backsurface of the image pickup apparatus 100 or on other location. Thecontrol circuit of the shutter 103 controls the shutter 103 based on ashutter drive signal 118 from the camera microcomputer 101. In thisembodiment, the shutter 103 is a known focal-plane shutter. The controlcircuit of the shutter 103 controls a shutter drive magnet, whichconstitutes the focal-plane shutter, to cause a shutter curtain totravel, thereby performing an exposure operation. The shutter 103 alsoincludes a photo interrupter configured to detect a position of a bladeof the shutter 103 to detect a timing of shutter travel completion andthe like. The photo interrupter is connected to the camera microcomputer101 via a signal line 119 configured to transmit a detection signal.

A photometry circuit 106 (a photometry unit) performs a calculation incooperation with a signal processing circuit 111 (a digital signalprocessing circuit) with respect to the image signal captured by theimage pickup element 102 to perform photometry processing. That is, thephotometry circuit 106 performs the photometry by using the signalobtained from the image pickup element 102. As described later, thephotometry is performed based on the signal from the image pickupelement 102 driven at a low frame rate.

A focus detection circuit 107 performs a calculation in cooperation withthe signal processing circuit 111 with respective to an image signalcaptured by the image pickup element 102 to perform focus detectioncontrol (AF control). That is, the focus detection circuit 107 performsthe focus detection by the contrast method based on the signal obtainedfrom the image pickup element 102. As described later, the focusdetection by the contrast method is performed based on a signal from theimage pickup element 102 driven at a high frame rate.

A gain switching circuit 108 switches a gain of a signal (anamplification signal) of the image pickup element 102. The switching ofthe gain is controlled by the camera microcomputer 101 depending on ashooing condition or a user's input operation. An A/D converter 109converts an amplified analog signal sent from the image pickup element102 to a digital signal. A timing generator 110 (a TG) has aconfiguration to synchronize a timing of inputting the amplificationsignal of the image pickup element 102 and a timing of the conversion bythe AD converter 109. The signal processing circuit 111 performs,depending on a parameter, image processing for the image data convertedby the A/D converter 109 to the digital signal. The description of astorage unit such as a memory configured to store a processed image willbe omitted.

A mount 130 configured to mount the lens unit 200 on the image pickupapparatus 100 includes a camera mount 130 a located on the image pickupapparatus 100 and a lens mount 130 b located on the lens unit 200. Themount 130 includes a communication terminal which enables datacommunication between the camera microcomputer 101 and a lensmicrocomputer 201, which is capable of performing the communicationbetween the camera microcomputer 101 and the lens microcomputer 201.This communication allows the camera microcomputer 101 to determine atype and a state of the lens unit 200 mounted on the image pickupapparatus 100.

An input portion 112 includes a release button (an SW1 and an SW2), anda switch, a button, a dial, or the like to switch modes of a singleshooting mode and a continuous shooting mode and is capable of inputtinga setting of the image pickup apparatus 100 and the like from theoutside. The display unit 113 includes a liquid crystal device, a lightemitting device, or the like configured to display various set modes andother shooting information. In addition, the display unit 113 displaysan image from the image pickup element 102 driven at a low frame rate asa live view.

Subsequently, the configuration and operation of the lens unit 200 willbe described. Reference numeral 201 denotes the lens microcomputer (acontroller or an LPU) configured to control the operation of eachcomponent of the lens unit 200. The lens microcomputer 201 performs acontrol of the lens unit 200 and various condition determinations. Thelens 202, which is constituted by a plurality of lenses, includes afocus lens configured to perform focusing by moving in an optical axisdirection. A lens drive unit 203 moves the focus lens of the lens 202 ina direction along an optical axis OA (an optical axis direction). Thecamera microcomputer 101 calculates a drive amount of the lens 202 basedon an output of the focus detection circuit 107 of the image pickupapparatus 100.

An encoder 204 detects a position (position information) of the lens202. The drive amount of the lens 202 calculated by the cameramicrocomputer 101 is communicated from the camera microcomputer 101 tothe lens microcomputer 201. Then, the lens microcomputer 201 performs adrive control for the lens drive unit 203 by using the positioninformation of the lens 202 and the drive amount calculated by thecamera microcomputer 101. The lens drive unit 203 moves the focus lensto an in-focus position in such a manner. In the focus detection, thecamera microcomputer 101 communicates a drive direction and a drivespeed of the focus lens to the lens microcomputer 201 and performs adrive control suitable for the focus detection operation (focus control)for the focus lens. That is, the camera microcomputer 101 (the lensmicrocomputer 201) performs focus drive of the focus lens based on adetection result of the focus detection circuit 107.

A stop 205 is used for adjusting a light intensity. A stop drive circuit206 drives the stop 205. The lens microcomputer 201 controls the stopdrive circuit 206 to perform the drive control of the stop 205. A stopdrive amount required to control the stop 205 is notified from thecamera microcomputer 101 to the lens microcomputer 201 by communication.While a focal length of the lens 202 is fixed (a single focus) in thisembodiment, applicable focal lengths are not limited to this and a focallength of the lens 202 may be variable as in the case of a zoom lens.

Next, referring to FIG. 2, the AF control performed by the focusdetection circuit 107 and the camera microcomputer 101 will bedescribed. FIG. 2 is an explanatory diagram of the AF control (focusdetection and focus drive) in this embodiment.

First, the focus detection circuit 107 receives, from the signalprocessing circuit 111, a contrast evaluation value (A) with respect toan image pickup signal (an image signal). The contrast evaluation value(A) is determined by the signal processing circuit 111 by extracting ahigh frequency component from the image pickup signal and thenintegrating the extracted high frequency component. In parallel withthis, the camera microcomputer 101 communicates with the lensmicrocomputer 201 to drive the focus lens via the lens drive unit 203.The camera microcomputer 101 (the focus detection circuit 107) searchesa position at which the contrast evaluation value reaches a peak (a peakposition) in such a manner (performs a peak value search). Upondetermination of the peak position of the contrast evaluation value, thecamera microcomputer 101 communicates with the lens microcomputer 201 todrive the focus lens toward the peak position (performs focus drive(C)).

That is, the focus detection circuit 107 obtains a contrast evaluationvalue (a focus signal) based on the signal from the image pickup element102 while moving the focus lens. Then, the focus detection circuit 107detects a position of the focus lens at which the contrast evaluationvalue reaches a peak (a position at which an in-focus state can beobtained). Subsequently, the camera microcomputer 101 performs the focusdrive so as to move the focus lens to an in-focus position. The AFcontrol completes when the above operations have been performed.

Next, the AF control and the photometry processing in the firstembodiment of the present invention will be described.

First, referring to FIG. 3, operation timings of the AF control and thephotometry processing in this embodiment will be described. FIG. 3 is anexplanatory diagram of the operation timings of the AF control and thephotometry processing. In FIG. 3, symbol SW1 denotes a status (on oroff) of the SW1 in which a shutter button is pressed halfway. Symbol VDdenotes a vertical synchronization signal (a VD signal) generated by thetiming generator 110 (the TG) that indicates a timing at which a pixelsignal is read from the image pickup element 102, that is, a frameperiod. Symbol AE denotes a timing at which the photometry circuit 106performs the photometry processing (i.e. accumulation, reading, andcalculation). Symbol AF denotes a timing at which the focus detectioncircuit 107 performs the AF control (i.e. peak value search (B) andfocus drive (C)).

In FIG. 3, a period F1 is a live-view operation period during a standbystate (a period in which the SW1 is turned off). In the period F1, aframe rate (a low-speed frame rate or a low frame rate) defined by thevertical synchronization signal is 30 fps. In the period F1, a low-speedframe rate of 30 fps is set as a frame rate at which a long-timelive-view operation can be continued, taking a consumption current ofthe image pickup apparatus 100, and a temperature rise in the imagepickup element 102 or the signal processing circuit 111 intoconsideration. Applicable frame rates, however, are not limited to thisand thus a frame rate other than 30 fps may be set as a low-speed framerate.

When the SW1 is turned on by the half press of the shutter buttonincluded in the input portion 112, the camera microcomputer 101 switchesa frame rate to a high-speed frame rate (a high frame rate) of 120 fpsto start the AF control (frame (m)). In this situation, an operation toturn the SW1 on (a predetermined operation) can be rephrased as anoperation to instruct shooting preparation or an operation to instructfocusing. In FIG. 3, a period F2 is a period in which a frame rate is120 fps (a period in which a frame rate is set to a high-speed framerate). In the period F2, the camera microcomputer 101 (the focusdetection circuit 107) obtains a contrast evaluation value (A) at aframe period of high-speed frame rate while driving the focus lens.Obtaining a contrast evaluation value at a high-speed frame rate enablesthe focus lens to be driven at a higher speed for the peak value search(B). This allows a reduction in time required for the focus detectionprocessing (contrast AF). While the high-speed frame rate set during theAF control is 120 fps in this embodiment, applicable frame rates are notlimited to this. Any frame rate other than 120 fps may be set as long asit is higher than that set during the standby state (the period F1).

Upon completion of the peak value search (B) for the contrast evaluationvalues by the focus detection circuit 107, the camera microcomputer 101returns the frame rate to 30 fps (the low-speed frame rate) as a framerate set for the standby state. In FIG. 3, a period F3 is a period whichstarts from when the high-speed frame rate is changed to the low-speedframe rate (a period after completion of the peak value search (B)). Inthe period F3, the camera microcomputer 101 returns the frame rate tothe low-speed frame rate (30 fps) and drives the focus lens toward aposition which represents a peak P of the contrast evaluation value (A).In FIG. 3, a period A2 represents a period of a series of AF controloperations including the peak value search (B) and the focus drive (C).At a right-end timing in the period A2, the AF control completes,satisfying a shooting condition for the AF.

Upon switching of the frame rate to 30 fps which is the low-speed framerate, the photometry circuit 106 starts the photometry processing beforecompletion of the AF control (in the period A2). When switching theframe rate, several processing such as settings of an accumulation timefor the photometry and a gain for reading are required. Therefore, theprocessing required to switch the frame rate is performed in a period B.After that, the photometry circuit 106 performs the photometryprocessing in the period A1. The photometry circuit 106 reads pixel dataaccumulated in a frame (n) and also performs a calculation in asubsequent frame (n+1). The camera microcomputer 101 determines anexposure parameter for shooting based on a result of the calculation.The photometry processing completes at the right-end timing in theperiod A1 and then the exposure parameter for shooing is prepared in aframe (n+2). Thus, the condition for the AE control can be satisfied.

As described above, the camera microcomputer 101 becomes ready for ashooting upon satisfaction of both of the shooting condition for the AFcontrol and that for the AE control. In FIG. 3, a period R represents aperiod in which a shooting can be performed. When the SW2, whichrepresents the full press of the shutter button that is included in theinput portion 112 and not illustrated in the drawing, is turned on at atiming earlier than a starting point (a left end) of the period R, ashooting operation starts at a timing indicated by the starting point ofthe period R. On the other hand, when the SW2 is turned on in the periodR, the shooting operation starts immediately.

Subsequently, referring to FIG. 4, the flow of the AF control and thephotometry processing in this embodiment will be described. FIG. 4 is aflowchart illustrating the AF control and the photometry processing.Each step of FIG. 4 is performed mainly by the photometry circuit 106 orthe focus detection circuit 107 based on a command (an instruction) ofthe camera microcomputer 101.

First, at step S101, the camera microcomputer 101 sets a low-speed framerate (30 fps in this embodiment) applied during the standby state as aframe rate for the live view. In addition, the camera microcomputer 101makes settings required for the timing generator 110.

Subsequently, at step S102, the photometry circuit 106 performs thephotometry. The photometry circuit 106 is capable of performing thephotometry in every frame in synchronization with the verticalsynchronization signal (the VD signal). This embodiment, however, is notlimited to this and the photometry circuit 106 may be configured so asto periodically (cyclically) perform the photometry processing, forexample, only once in several frames, taking a processing load of thesystem (the image pickup apparatus) into consideration.

Subsequently, at step S103, the camera microcomputer 101 determineswhether or not the SW1 is turned on. When the camera microcomputer 101determines that the SW1 is off, it repeats step S102 while waiting foran input of the shutter button. On the other hand, when the cameramicrocomputer 101 determines that the SW1 is turned on, the flowproceeds to step S104.

Subsequently, at step S104, the camera microcomputer 101 performs aframe rate switching, that is, a switching from a low-speed frame rate(a low frame rate) to a high-speed frame rate (a high frame rate). Inthis embodiment, the camera microcomputer 101 performs the switchingfrom a frame rate of 30 fps to a frame rate of 120 fps. The switching ofthe low-speed frame rate to the high-speed frame rate in such a mannershortens the contrast evaluation value sampling period, which enablesthe focus lens to be driven at higher speed for the peak value search.This allows a reduction in processing time of the contrast AF.

After the switching to the high-speed frame rate, at step S105, thecamera microcomputer 101 performs an AF exposure control such that anappropriate exposure is achieved for an AF frame (the periphery of an AFframe) selected by a user. The AF exposure control is performed in theframe (m) of the VD signal illustrated in FIG. 3. More specifically, thecamera microcomputer 101 determines, based on a result of the photometryperformed in the period F1, whether or not the appropriate exposure isachieved for blocks adjacent to the AF frame. When the cameramicrocomputer 101 determines that the exposure for the blocks isdifferent by 1EV or more from the appropriate exposure, it performs theexposure control (the AE control). The exposure control may be performedby using any of an accumulation time, a read gain, and a stop of thelens unit. This causes a contrast evaluation value for the focusdetection to be output as a value which has an appropriate level evenwhen an object to be focused is darker compared with other regions in ascreen. On the other hand, during the standby state, the AE control isperformed taking a brightness of the entire screen into consideration.This may result in a difference between an exposure for the live viewduring the standby state and an exposure during the AF processing.

Subsequently, at step S106, the camera microcomputer 101 starts a searchdrive, that is, a peak search for contrast evaluation values. Then, atstep S107, the focus detection circuit 107 obtains a contrast evaluationvalue (an AF evaluation value). In the search drive, the cameramicrocomputer 101 moves the focus lens while obtaining the contrastevaluation value and detects a position of the focus lens at which thecontrast evaluation value reaches a peak (a peak position of the focuslens). After that, at step S108, the camera microcomputer 101 determineswhether or not the focus detection circuit 107 detects the position ofthe focus lens at which the contrast evaluation value (the AF evaluationvalue) reaches the peak. When the camera microcomputer 101 determinesthat the focus detection circuit 107 does not detect the peak positionof the focus lens, it repeats step S107 until the focus detectioncircuit 107 detects the peak position. On the other hand, when thecamera microcomputer 101 determines that the focus detection circuit 107detects the peak position of the focus lens, the flow proceeds to stepS109. At step S109, the camera microcomputer 101 stops the drive of thefocus lens for the peak search started at step S106.

Subsequently, the camera microcomputer 101 performs, in parallel, aframe rate switching at step S110 and a focus dive (the drive of thefocus lens to an in-focus position) at step S112. That is, the cameramicrocomputer 101 switches a frame rate in the focus drive. At stepS110, the camera microcomputer 101 changes the high-speed frame rate(120 fps) to a normal frame rate that is set for the live view (thelow-speed frame rate: 30 fps). In addition, the camera microcomputer 101returns a status of the AF exposure control performed at step S105 to anoriginal status while changing the frame rate. For instance, the cameramicrocomputer 101 stores, at step S105, an exposure control value (anexposure control parameter) set before the change to the AF exposurecontrol in a memory (a storage unit) located inside the cameramicrocomputer 101. Then, at step S110, the camera microcomputer 101changes the exposure control parameter to be used in the AF exposurecontrol to the exposure control parameter stored in the memory. Thisembodiment, however, is not limited to this and other methods may beused to change an exposure control status.

After the camera microcomputer 101 changes the frame rate to thelow-speed frame rate (30 fps), the photometry circuit 106 performs thephotometry processing at step S111. In this embodiment, the photometrycircuit 106 performs evaluation photometry by weighting a focusdetection region used for the detection of an in-focus frame (anin-focus point position), i.e. the photometry circuit 106 performs thephotometry processing based on a signal corresponding to the focusdetection region. This embodiment, however, is not limited to this andthe photometry circuit 106 may perform averaged photometry in which theentire screen is averaged. Alternatively, if a photometry method can beselected by a user, the photometry circuit 106 may perform thephotometry according to the photometry method set by the user. Thecamera microcomputer 101 calculates the exposure parameters for stillimage shooting (e.g. TV, AC, ISO) and stores these values in the memory(the storage unit) located inside the camera microcomputer 101 toperform the exposure control for the still image shooting based on adetected photometry result. The completion of the photometry processingat step S111 leads to satisfying the shooting condition for the AEcontrol.

On the other hand, at step S112, the camera microcomputer 101 drives thefocus lens to a position at which the contrast evaluation value reachesa peak (an in-focus position). The completion of the AF control at stepS112 leads to satisfying the shooting condition for the AF control.

After completion of the photometry processing at step S111 and the AFcontrol at step S112, the camera microcomputer 101 permits, at stepS113, to accept the SW2, which represents the full press of the shutterbutton included in the input portion 112 (release permission). Thisenables to perform a shooting at any timing not sooner than that timing.That is, the camera microcomputer 101 completes the photometryprocessing by the photometry circuit 106 and then performs the controlsuch that a shooting operation can be performed (permits shootingprocessing). During the shooting, the camera microcomputer 101 (thephotometry circuit 106) can perform an appropriate exposure control byusing the exposure control parameters stored in the memory at step S111.

In this embodiment, the timing generator 110 switches a frame rate ofthe image pickup element 102 from the high-speed frame rate to thelow-speed frame rate in parallel with the drive of the focus lens by thecamera microcomputer 101 to an in-focus position. Subsequent to theframe rate switching, the photometry circuit 106 performs the photometryprocessing based on a signal from the image pickup element 102.Preferably, the photometry circuit 106 accumulates the signal from theimage pickup element 102 for the exposure control after the focusdetection while the camera microcomputer 101 drives the focus lens tothe in-focus position (a frame (n) of FIG. 3).

Further preferably, when the SW1 of the input portion 112 is turned onwhile the image pickup element 102 is driven at the low-speed framerate, the timing generator 110 switches the low-speed frame rate to thehigh-speed frame rate to drive the image pickup element 102. Upondetection of the in-focus position, the timing generator 110 switchesthe high-speed frame rate to the low-speed frame rate to drive the imagepickup element 102.

This embodiment performs the frame rate switching and the photometryprocessing for the AE control in parallel with the focus drive of thefocus lens in the AF control, which enables a high-speed shootingoperation (reduction in time lag) with suppressed consumption currentand temperature rise.

Second Embodiment

Next, AF control and photometry processing in the second embodiment ofthe present invention will be described.

There are various interchangeable lenses (the lens unit 200) possible tobe employed as an interchangeable lens system. In addition, lens unitswhich change an image magnification of an object by a focusing operationare known. A change in the image magnification causes a change in a sizeof an object image on an imaging plane near the center of the screen,and a change in the size and a movement in a position of the objectimage at the periphery of the screen.

In the first embodiment, the configuration has been described in whichthe frame rate switching and the photometry processing are performed inthe focus drive of the image pickup lens. When a lens unit whose imagemagnification significantly varies is used in the configuration of thefirst embodiment, performing the photometry during the focus drive ofthe focus lens is likely to derive a photometry result different fromthat derived in an in-focus state. Thus, in this embodiment, aconfiguration will be described in which a frame rate is switched duringthe focus drive of the image pickup lens and the photometry is performedafter the focus drive.

First, referring to FIG. 5, operation timings of the AF control and thephotometry processing in this embodiment will be described. FIG. 5 is anexplanatory diagram of the operation timings of the AF control and thephotometry processing. In FIG. 5, a description for the same parts asthose of the first embodiment (FIG. 3) will be omitted.

In FIG. 5, upon completion of the frame rate switching, that is, at aright-end timing in a period B, the image pickup apparatus comes into astate in which it can start the photometry. In this embodiment, thestart of the photometry processing, however, is delayed in order toavoid an influence of change in image magnification due to the focusdrive of the focus lens. This embodiment, however, is not limited tothis. For instance, the image pickup apparatus may be configured suchthat the photometry processing is performed in each frame subsequent toa frame (n−1) and a result thereof is not used for determining exposurecontrol parameters.

After completion of the focus drive in the AF control, that is, in aframe (n) following a period A2, the photometry circuit 106 starts thephotometry processing. The photometry circuit 106, in a frame (n+1),reads pixel data accumulated in the frame (n) and performs a calculationfor the pixel data to determine the exposure control parameters forshooting. The photometry processing completes at an end-point(right-end) timing of the period A1 and the exposure control parametersfor shooting are prepared in frames subsequent to a frame (n+2). Thisleads to satisfying a shooting condition for the AE control. Uponcompletion of this series of processing, the image pickup system comesinto a state in which it can perform the shooting (a period R).

Next, referring to FIG. 6, the flow of the AF control and the photometryprocessing in this embodiment will be described. FIG. 6 is a flowchartillustrating the AF control and the photometry processing. Each step ofFIG. 6 is performed mainly by the photometry circuit 106 or the focusdetection circuit 107 based on a command (an instruction) of the cameramicrocomputer 101. Since steps S201 to S209 of FIG. 6 are the same assteps S101 to S109 of FIG. 4 described in the first embodiment,respectively, the description thereof will be omitted.

At step S209 of FIG. 4, the camera microcomputer 101 stops the drive ofthe focus lens for the peak value search started at step S206.Subsequently, the camera microcomputer 101 performs a frame rateswitching at step S210 and a focus drive at step S211 (the drive of thefocus lens to an in-focus position) in parallel. That is, the cameramicrocomputer 101 switches a frame rate during the focus drive. Sincesteps S210 and S211 of FIG. 4 are the same as steps S110 and S112,respectively, the detailed description thereof will be omitted.

After completion of the frame rate change at step S210 and the AFcontrol at step S211, the photometry circuit 106 performs the photometryprocessing at step S212. After completion of the photometry processingat step S212 (and the AF control at step S211), the camera microcomputer101 permits, at step S213, to accept the SW2, which represents the fullpress of the shutter button included in the input portion 112 (releasepermission). This enables to perform a shooting at any timing not soonerthan that timing (the camera microcomputer 101 permits shootingprocessing). During shooting, the camera microcomputer 101 (thephotometry circuit 106) can perform an appropriate exposure control byusing the exposure control parameters stored in the memory at step S212.

As described above, in this embodiment, the photometry circuit 106performs the photometry processing based on a signal from the imagepickup element 102 after the camera microcomputer 101 completes thefocus drive of the focus lens.

In this embodiment, the frame rate switching is performed in parallelwith the focus drive of the focus lens in the AF control and thephotometry processing is performed upon completion of the focus drive.This enables a high-speed shooting operation (reduction in time lag)with suppressed consumption current and temperature rise while reducingan influence of a change in image magnification.

Third Embodiment

Next, referring to FIG. 7, the configuration of an image pickupapparatus in the third embodiment of the present invention will bedescribed. FIG. 7 is a block diagram illustrating the configuration ofthe image pickup apparatus in the third embodiment. While, in thisembodiment, an image pickup system will be described in which a lensunit 700 (a lens apparatus) is removably attached to a camera body 720as the image pickup apparatus, applicable configurations are not limitedto this. This embodiment is applicable also to an image pickup apparatusconstituted by the camera body 720 and the lens unit 700 integrated witheach other.

In the lens unit 700 of FIG. 7, a first lens unit 701 is disposed at afront end of the lens unit 700 and held movably forward and backward ina direction along an optical axis OA (an optical axis direction). A stop702 adjusts light intensity during shooting by adjusting its openingdiameter. The stop 702 and a second lens unit 703 move forward andbackward in the optical axis direction in an integrated manner andachieve a zoom function in conjunction with the forward and backwardmovement of the first lens unit 701. A third lens unit 704 (a focuslens) performs focusing by moving forward and backward in the opticalaxis direction.

A zoom actuator 711 drives the first lens unit 701 and the second lensunit 703 to move forward and backward in the optical-axis direction toperform a zoom operation. A stop actuator 712 includes a stepping motorand the like. A focus actuator 713 drives the third lens unit 704 tomove forward and backward in the optical axis direction to perform thefocusing. A zoom drive circuit 714 drives the zoom actuator 711 inresponse to a zoom operation by a user. A stop drive circuit 715 drivesthe stop actuator 712 to control an opening of the stop 702. A focusdrive circuit 716 performs a drive control of the focus actuator 713based on a focus detection result and drives the third lens unit 704 tomove forward and backward in the optical axis direction to perform thefocusing.

A lens microcomputer 717 (a controller) performs all calculations andcontrols for the lens unit 700. The lens microcomputer 717 controls thezoom drive circuit 714, the stop drive circuit 715, the focus drivecircuit 716, and a lens memory 718. In addition, the lens microcomputer717 detects a current position of each lens unit and notifies a cameramicrocomputer 725 of lens position information in response to a command(an instruction) from the camera microcomputer 725. The lens memory 718stores optical information required for auto focusing. The lens unit 700is attached to the camera body 720 via a mount 710.

In the camera body 720, an optical low-pass filter 721 is an opticalelement to reduce a false color or a moire of a shot image. An imagepickup element 722 configured to photoelectrically convert an objectimage (an optical image) includes a CMOS sensor (or a CCD sensor) and aperipheral circuit thereof. In the image pickup element 722, onephotoelectric conversion element is placed on each light receiving pixelthat has m pixels in a horizontal direction and n pixels in a verticaldirection, and focus detection pixel lines are discretely arranged.

An image pickup element drive circuit 723 (a drive unit) controls animage pickup operation of the image pickup element 722, and performs A/Dconversion on an image signal output from the image pickup element 722to send a digital image signal to the camera microcomputer 725. Inaddition, the image pickup element drive circuit 723 switches a framerate (a drive frame rate) of the image pickup element 722 in response toa command (an instruction) of the camera microcomputer 725.

An image processing circuit 724 performs various image processing suchas gamma conversion, color interpolation, and JPEG compression for theimage signal output from the image pickup element 722. A display 726 (adisplay unit) such as an LCD displays information on a shooting mode ofthe camera body 720, a pre-view image before shooting and an image to bechecked after shooting, an in-focus-state display image at the time ofthe focus detection, and the like. In addition, the display 726 displaysan image sent from the image pickup element 722 driven at a low-speedframe rate (a low frame rate) as a live view. An operating SW 727 (anoperating switch group) includes a power switch, a release (shootingtrigger) switch, a zoom operation switch, a shooting mode selectionswitch, and the like. In this embodiment, the operating SW furtherincludes an AF start button to perform the auto focusing (AF control).

A removable memory 728 (a flash memory) records a shot image. Animaging-plane phase-difference focus detection unit 729 performs focusdetection by a phase difference method by using a signal obtained fromthe focus detection pixel of the image pickup element 722. A contrastfocus detection unit 730 performs focus detection processing by acontrast method by using a contrast evaluation value generated from ahigh frequency component of an image obtained by the image processingcircuit 724. In this embodiment, the contrast focus detection unit 730performs the focus detection by the contrast method while the imagepickup element drive circuit 723 drives the image pickup element 722 ata high-speed frame rate (a high frame rate).

The camera microcomputer 725 (a controller) performs all calculationsand controls in the camera body 720. The camera microcomputer 725controls the image pickup element drive circuit 723, the imageprocessing circuit 724, the display 726, the operating SW 727, thememory 728, the imaging-plane phase-difference focus detection unit 729,and the contrast focus detection unit 730. The camera microcomputer 725communicates with the lens microcomputer 717 via a signal line of themount 710 to send a request for obtaining the lens position informationand for driving each lens at a predetermined drive amount to the lensmicrocomputer 717. The camera microcomputer 725 is capable of obtainingoptical information unique to each lens unit 700 (an interchangeablelens). The camera microcomputer 725 includes a ROM configured to store aprogram to control an operation of the camera body 720, a RAM configuredto store a variable, and an EEPROM (electrically erasable programmableread-only memory) configured to store various parameters. Moreover, thecamera microcomputer 725 performs focus detection processing describedlater (control of the image pickup apparatus) according to the programstored in the ROM.

In this embodiment, the image pickup element 722 includes an imagepickup pixel and a focus detection pixel. The imaging-planephase-difference focus detection unit 729 performs the focus detectionby the phase difference method (imaging-plane phase-difference AF) basedon an image shift amount of a pair of images formed on the focusdetection pixels by light beams which pass through pupil regions(divided pupil regions) different from each other.

Next, referring to FIGS. 9A and 9B to 12, the imaging-planephase-difference AF will be described. FIGS. 9A and 9B to 11A and 11Bare diagrams explaining the configurations of the image pickup pixel andthe focus detection pixel. This embodiment adopts a Bayer arrayconstituted by repetition of 4 (2×2) pixels, in which two pixels havinga spectral sensitivity to G (green) are arranged at two diagonal pixelpositions and one pixel having a spectral sensitivity to R (red) and onepixel having a spectral sensitivity to B (blue) are arranged at theother two pixel positions. In the Bayer array, the focus detectionpixels having a configuration described later are arranged discretelyaccording to a predetermined rule.

FIGS. 9A and 9B illustrate the arrangement and the structure of theimage pickup pixels. FIG. 9A is a plan view of the image pickup pixelsarranged in two columns and two rows. As generally known, in the Bayerarray, G pixels are arranged in a diagonal direction and an R pixel anda B pixel are arranged at the other two pixel positions. The structureof the two columns and the two rows is repeatedly arranged.

FIG. 9B is a cross-sectional view illustrating a section A-A of FIG. 9A.Symbol ML denotes an on-chip micro lens disposed on the front of eachpixel, symbol CF_(R) denotes an R (Red) color filter, and symbol CF_(G)denotes a G (Green) color filter. Symbol PD denotes a photoelectricconversion portion of the CMOS sensor which is schematicallyillustrated, and symbol CL denotes a wiring layer to form a signal lineconfigured to transmit various signals in the CMOS sensor. Symbol TLdenotes an image pickup optical system (an image pickup lens) which isschematically illustrated.

The on-chip micro lens ML of each image pickup pixel and thephotoelectric conversion portion PD are configured so as to capture, aseffectively as possible, a light beam passing through the image pickupoptical system TL. In other words, an exit pupil EP of the image pickupoptical system TL, and the photoelectric conversion portion PD have aconjugate relation to each other by the micro lens ML, and thephotoelectric conversion portion PD is designed to have a largeeffective area. While the incident light beam on the G pixel isdescribed in FIG. 9B, the R pixel and the B (blue) pixel also have thesame structure. Accordingly, the exit pupil EP corresponding to each ofthe image pickup pixels R, G, and B has a large diameter, and the lightbeam from an object is effectively captured to improve a signal to noiseratio (S/N) of an image signal.

FIGS. 10A and 10B illustrate the arrangement and the structure of thefocus detection pixel to perform the pupil division in a horizontaldirection (an x direction) of the image pickup optical system TL (theimage pickup lens). The “horizontal direction (x direction)” as used inthis embodiment means a direction along a straight line which isorthogonal to an optical axis and extends horizontally when the camerais held such that the optical axis of the image pickup optical system TLis horizontal. FIG. 10A is a plan view of pixels of two columns and tworows including the focus detection pixels. When obtaining an imagesignal for use in recording or viewing, a main component of brightnessinformation is obtained by the G pixels. Since the image recognitioncharacteristics of human are sensitive to brightness information, imagedeterioration is easy to be recognized when the G pixel is defective. Onthe other hand, since the visual perception of human is insensitive tocolor information, image deterioration is difficult to be recognizedwhen the R and B pixels, which are pixels configured to obtain colorinformation (color difference information), are used even if the pixelto obtain the color information is defective to some extent. Therefore,in this embodiment, the G pixels of the two columns and the two rowsremain as the image pickup pixels and the R and B pixels are replaced bythe focus detection pixels. In FIG. 10A, the focus detection pixels aredenoted by symbols S_(HA) and S_(HB).

FIG. 10B is a cross-sectional view illustrating a section B-B in FIG.10A. The micro lens ML and the photoelectric conversion portion PD havethe same structures as those of the image pickup pixels illustrated inFIG. 9B. Since signals of the focus detection pixels are not used forgenerating an image in this embodiment, a transparent film CF_(w)(White) is placed instead of a color filter for separating colors. Inorder to perform the pupil division with the image pickup element 722,openings of the wiring layer CL are eccentric with respect to the centerlines of the corresponding micro lenses MLs in one direction (in the xdirection). More specifically, since an opening OP_(HA) of the pixelS_(HA) is eccentric rightward (in a −x direction), the pixel S_(HA)receives a light beam that has passed through a left-side exit pupilEP_(HA) of the image pickup optical system TL. Similarly, since anopening OP_(HB) of the pixel S_(HB) is eccentric leftward (in a +xdirection), the pixel S_(HB), receives a light beam that has passedthrough a right-side exit pupil EP_(HB) of the image pickup opticalsystem TL. The pixels S_(HA) are regularly arranged in the horizontaldirection (in the x direction), and an object image obtained by thepixels S_(HA) is defined as an A image. Similarly, the pixels S_(HB) areregularly arranged in the horizontal direction (in the x direction), andthe object image obtained by the pixels S_(HB) is defined as a B image.The calculation of relative positions of the A image and the B imageallows detecting a focus shift amount (a defocus amount) of the objectimage.

While, in the pixels S_(HA) and S_(HB), it is possible to perform thefocus detection for an object which has a brightness distribution in thex direction of a shooting screen, e.g. a vertical line (a line in a ydirection), it is impossible to perform the focus detection for ahorizontal line (a line in the x direction) which has a brightnessdistribution in a vertical direction (the y direction). In thisembodiment, in order to make it possible to perform the focus detectionfor the latter, pixels configured to perform the pupil division in avertical direction (the y direction) of the image pickup optical systemTL are also provided.

FIGS. 11A and 11B illustrate the arrangement and the structure of thefocus detection pixels to perform the pupil division in the verticaldirection (the y direction) of the image pickup optical system TL. The“vertical direction (the y direction)” as used in this embodiment meansa direction along a straight line which is orthogonal to the opticalaxis and extends vertically when the camera is held such that theoptical axis of the image pickup optical system TL is horizontal. FIG.11A is a plan view of pixels of two columns and two rows including thefocus detection pixels, and as in the case of FIG. 10A, the G pixelsremain to be image pickup pixels and the R and B pixels are the focusdetection pixels. In FIG. 10A, the focus detection pixels are denoted bysymbols S_(VC) and S_(VD).

FIG. 11B is a cross-sectional view illustrating a section C-C of FIG.11A. In contrast to the pixels of FIG. 10B having the structure todivide the pupil in the horizontal direction (the x direction), thepixels of FIG. 11B have a structure to divide the pupil in the verticaldirection (the y direction). The structure of other pixels of FIG. 11Bis the same as that of FIG. 10B. That is, since an opening OP_(VC) of apixel S_(VC) is eccentric downward (in a −y direction), the pixel S_(VC)receives a light beam that has passed through an upper-side (+ydirection) exit pupil EP_(VC) of the image pickup optical system TL.Similarly, since an opening OP_(VD) of a pixel S_(VD) is eccentricupward (in a +y direction), the pixel S_(VD) receives a light beam thathas passed through a right exit pupil EP_(VD) of the image pickupoptical system TL. The pixels S_(VC) are arranged regularly in thevertical direction (the y direction), and an object image obtained bythese pixels (pixel group) is defined as a C image. Similarly, thepixels S_(VC) are arranged regularly in the vertical direction (the xdirection), and the object image obtained by these pixels (pixel group)is defined as a D image. The detection (calculation) of a relativeposition between the C image and the D image allows detecting a focusshift amount (a defocus amount) of the object image.

In addition, as the difference between an eccentricity amount of theopening OP_(VC) of the pixel S_(VC) and that of the opening OP_(VD) ofthe pixel S_(VD) is larger, the sensitivity with respect to thedefocusing becomes higher and the focus detection accuracy is improved.In contrast, when a large amount of defocusing occurs, an image shiftamount becomes large and the maximum defocus range in which the focusdetection can be performed relatively becomes small. The arrangement ofeither of the focus detection pixels for horizontal-direction detectionor those for vertical-direction detection illustrated in FIGS. 10A, 10B,11A, and 11B, which are focus detection systems having differentcharacteristics, enables an improvement in focusing accuracy.

FIG. 12 is a diagram conceptually explaining a pupil division situationof the image pickup element 722 in this embodiment. In FIG. 12, symbolTL denotes an image pickup lens, reference numeral 722 denotes the imagepickup element, symbol OBJ denotes an object, and symbol IMG denotes anobject image. As described with reference to FIGS. 9A and 9B, the imagepickup pixel receives a light beam that has passed through the entireregion of the exit pupil EP of the image pickup optical system TL. Onthe other hand, as described with reference to FIGS. 10A, 10B, 11A, and11B, the focus detection pixels have a pupil dividing function.

More specifically, the pixel S_(HA) illustrated in FIGS. 10A and 10Breceives a light beam that has passed through a pupil of a +x directionside, that is, a light beam L_(HA) that has passed through the pupilEP_(HA) illustrated in FIG. 12. Similarly, the pixels S_(HB), S_(VC),and S_(VD) receive light beams L_(HB), L_(VC), and L_(VD) that havepassed through pupils EP_(HB), EP_(VC), and EP_(VD), respectively. Thefocus detection pixels are distributed over the entire region of theimage pickup element 722, and therefore the focus detection can beperformed by the imaging-plane phase-difference AF. Moreover, since thefocus detection can be performed over the entire imaging region, aresult of the imaging-plane phase-difference AF can be obtained insynchronization with the contrast focus detection unit 730 in the sameranging frame (a focus detection frame) at an arbitrary position set bya user.

While a focus detection method using the imaging-plane phase-differenceAF is described as an example in this embodiment, applicable focusdetection methods are not limited to this as long as they are focusdetection methods which do not use a contrast evaluation value. Forinstance, a focus detection method which employs a phase differencedetection at the outside or active ranging may also be adopted. In thisembodiment, focus detection control and frame rate switching performedwhen an AF start button is operated will be mainly described and otherdescription will be omitted.

Next, referring to FIG. 8, the control of the image pickup apparatus inthis embodiment will be described. FIG. 8 is a flowchart illustratingthe control of the image pickup apparatus in this embodiment. Adescription will be given here of a series of operations triggered by anoperation of the AF start button performed at the time in a state inwhich a live-view image is displayed with the image pickup element 722being driven at a low-speed frame rate before the AF start button isoperated. Each step of FIG. 8 is performed mainly by the imaging-planephase-difference focus detection unit 729, the contrast focus detectionunit 730, or the image pickup element drive circuit 723 based on acommand (an instruction) of the camera microcomputer 725.

First, at step S301, when the AF start button (an operating SW 727) isnot operated by a user, the camera microcomputer 725 controls the imagepickup element drive circuit 723 so as to drive the image pickup element722 at a low-speed frame rate. In this situation, an image processed bythe image processing circuit 724 is displayed on the display 726 at alow-speed frame rate (live-view display). Subsequently, at step S302,the imaging-plane phase-difference focus detection unit 729 obtainsimage information for the imaging-plane phase-difference AF. At thistime, the camera microcomputer 725 obtains image informationcorresponding to a set ranging frame (a focus detection frame), which isnot illustrated in the drawing, from the imaging-plane phase-differencefocus detection unit 729. A contrast evaluation value, as well as theimage information, may be obtained.

Subsequently, at step S303, the camera microcomputer 725 determineswhether or not the user operates the AF start button (the SW 727). Thecamera microcomputer 725 starts the focus control (the AF control) inresponse to an operation of the AF start button. When the cameramicrocomputer 725 determines that the AF start button is not operated,it repeats steps S302 and S303. That is, the camera microcomputer 725continues to obtain the image information from the imaging-planephase-difference focus detection unit 729. On the other hand, when thecamera microcomputer 725 determines that the AF start button isoperated, the flow proceeds to step S304.

At step S304, the camera microcomputer 725 determines whether or not thelatest image information (a focus detection signal which is animaging-plane phase-difference AF output) obtained at step S302 has areliability. The reliability of the image information is determinedusing, for example, the S level (SELECT LEVEL) value disclosed in JP2007-052072. When the camera microcomputer 725 determines that thereliability of the imaging-plane phase-difference AF output is low, theflow proceeds to step S306. On the other hand, when the cameramicrocomputer 725 determines that the reliability of the imaging-planephase-difference AF output is high, the flow proceeds to step S305.

At step S305, the camera microcomputer 725 starts driving the focus lens(the third lens unit 704) from an in-focus position obtained as a resultof the imaging-plane phase-difference AF to a position apart from thein-focus position by a predetermined range of distance based on theimage information obtained at step S302. After that, at step S306, thecamera microcomputer 725 performs switching processing for switching aframe rate to a high-speed frame rate in order to perform the contrastAF control at a high speed. When the camera microcomputer 725determines, at step S304, that the reliability of the latest imageinformation which is obtained before the frame rate is switched is high,it switches the frame rate while moving the focus lens to a positionobtained from the image information. The position to which the focuslens is moved (the position apart from the in-focus position by apredetermined range of distance obtained based on the image information)corresponds to a position at which a scanning is started by the contrastAF to be performed at step S308. When an approximate in-focus positionis known in advance, an AF period of time can be shortened by starting ascanning operation from the periphery of an estimated in-focus position,instead of a scanning operation over the entire movable range of thefocus lens. In this embodiment, the predetermined range of distance isset to a value obtained experimentally or experientially so that thepeak of the contrast evaluation value can be satisfactorily detectedwhen the scanning operation is performed at the periphery of thein-focus position obtained based on the image information. Although anoutput signal from the image pickup element 722 cannot be obtainedduring the frame rate switching, in this embodiment, the focus lens isdriven to the scanning start position by using the image informationwhich is obtained before the frame rate is switched. Performing thiscontrol allows moving the focus lens to the scanning start positionbased on the in-focus position determined by the imaging-planephase-difference AF without waiting for the completion of the frame rateswitching, and therefore a period of time required for the focusdetection can be reduced.

At step S307, the camera microcomputer 725 controls the image pickupelement drive circuit 723 so as to drive the image pickup element 722 ata high-speed frame rate. At this time, the image processed by the imageprocessing circuit 724 is displayed on the display 726 at a high-speedframe rate. Subsequently, at step S308, the contrast focus detectionunit 730 performs the focus detection by the contrast method at ahigh-speed frame rate. In this situation, the camera microcomputer 725performs the scanning operation to move the focus lens while obtainingthe contrast evaluation value. As described above, the start position ofthe scanning operation is determined based on the in-focus positionobtained using the image information which is obtained before the framerate is switched. The focus lens is moved to a position at which thecontrast evaluation value reaches a peak based on a result of thescanning, and then the AF processing is completed.

As described above, the camera microcomputer 725 changes a frame rate ofthe image pickup element 722 from the low-speed frame rate to thehigh-speed frame rate when the focus control is performed. In this case,when the reliability of the image information (the focus detectionsignal) determined by the imaging-plane phase-difference AF is high, thecamera microcomputer 725 determines the scanning start position of thefocus control based on the image information. After that, the cameramicrocomputer 725 drives the focus lens to the scanning start positionwhile performing the frame rate switching.

According to the flowchart of FIG. 8, at the beginning of the focusdetection, the camera microcomputer 725 starts driving the focus lens tothe scanning start position based on a focus detection result (an outputresult of the imaging-plane phase-difference AF in this embodiment)obtained without using the contrast evaluation value. The cameramicrocomputer 725 switches the low-speed frame rate to the high-speedframe rate in parallel with the drive of the focus lens. This enables toperform a high-speed and smooth focus control.

In some cases, the low-speed frame rate may be switched to thehigh-speed frame rate while the focus lens is driven to the scanningstart position obtained based on the in-focus position determined by theimaging-plane phase-difference AF. In these cases, this embodimentenables to transfer to the focus control by the contrast AF withoutstopping the drive of the focus lens. This allows more smooth focuscontrol at higher speed.

Fourth Embodiment

Next, referring to FIG. 13, the configuration of an image pickupapparatus in the fourth embodiment of the present invention will bedescribed. FIG. 13 is a block diagram illustrating the configuration ofthe image pickup apparatus (an image pickup system) in this embodiment.The image pickup apparatus of this embodiment illustrated in FIG. 13 isdifferent from that of the third embodiment illustrated in FIG. 7 inthat it is not provided with the imaging-plane phase-difference focusdetection unit 729. Since other configuration is the same as theconfiguration of the image pickup apparatus of the third embodiment, thedescription thereof will be omitted.

The camera microcomputer 725 and the contrast focus detection unit 730perform the above-described scanning operation to detect a position ofthe focus lens at which a contrast evaluation value reaches a peak toperform the focus control. The contrast AF control, because of itsproperty, requires the focus lens to once leave a position near a peakof the contrast evaluation value in order to detect the peak when thefocus lens is located at the position near the peak at the time of thestart of the focus control. The control in which the focus lens leavesthe peak position of a contrast evaluation value is a control which doesnot require the contrast evaluation value. This embodiment relates to acontrol of switching the frame rate during this control.

Next, referring to FIG. 14, the control of the image pickup apparatus inthis embodiment will be described. FIG. 14 is a flowchart illustratingthe control of the image pickup apparatus in this embodiment. Adescription will be given here of a series of operations triggered by anoperation of the AF start button performed at the time in a state inwhich a live-view image is displayed with the image pickup element 722being driven at a low-speed frame rate before the AF start button isoperated. Each step of FIG. 14 is performed mainly by the contrast focusdetection unit 730 or the image pickup element drive circuit 723 basedon a command (an instruction) of the camera microcomputer 725.

First, at step S801, when the AF start button (the operating SW 727) isnot operated by a user, the camera microcomputer 725 controls the imagepickup element drive circuit 723 so as to drive the image pickup element722 at a low-speed frame rate. In this situation, an image processed bythe image processing circuit 724 is displayed on the display 726 at alow-speed frame rate (live-view display).

Subsequently, at step S802, the camera microcomputer 725 determineswhether or not the user operates the AF start button (the SW 727). Whenthe camera microcomputer 725 determines that the AF start button is notoperated, it repeats step S802. On the other hand, when the cameramicrocomputer 725 determines that the AF start button is operated, theflow proceeds to step S803. The camera microcomputer 725 continues toobtain contrast evaluation values until the AF start button is operated.

After that, at step S803, the camera microcomputer 725 determineswhether or not the focus lens (the third lens unit 704) is located anear in-focus position (performs a near in-focus-positiondetermination). For instance, when the latest contrast evaluation valueis higher than a predetermined threshold value, the camera microcomputer725 determines that the focus lens is located at the near in-focusposition. When the camera microcomputer 725 determines, at step S803,that the focus lens is not located at the near in-focus position, theflow proceeds to step S805. On the other hand, when the cameramicrocomputer 725 determines that the focus lens is located at the nearin-focus position, the flow proceeds to step S804.

When the camera microcomputer 725 determines, at step S803, that thefocus lens is located at the near in-focus position, it starts drivingthe focus lens at step S804 so as to move the focus lens to a positionapart from the near in-focus position by a predetermined range ofdistance.

At step S805, the camera microcomputer 725 performs the switchingprocessing for switching a frame rate to a high-speed frame rate inorder to perform the contrast AF control at high speed. When the cameramicrocomputer 725 determines, at step S803, that the focus lens islocated at the near in-focus position, it switches the frame rate whilemoving the focus lens to the position apart from the near in-focusposition by the predetermined range of distance. The position to whichthe focus lens is moved (the position apart from the near in-focusposition by the predetermined range of distance) corresponds to aposition at which a scanning is started by the contrast AF to beperformed at step S807. In this embodiment, the predetermined range ofdistance is set to a value obtained experimentally or experientially sothat the peak of the contrast evaluation value can be satisfactorilydetected when the scanning operation is performed at the periphery ofthe in-focus position. Although an output signal from the image pickupelement 722 cannot be obtained during the frame rate switching, in thisembodiment, whether or not the focus lens is located at the nearin-focus position is determined based on the contrast evaluation valueobtained before the frame rate switching is performed. When the cameramicrocomputer 725 determines that the focus lens is located at the nearin-focus position, it drives the focus lens to the position apart fromthe near in-focus position by the predetermined range of distance sothat the peak of the contrast evaluation value can be detected.Performing this control allows moving the focus lens from the positiondetermined to be located near the in-focus position to the scanningstart position without waiting for the completion of the frame rateswitching, and therefore a period of time required for the focusdetection can be reduced.

Subsequently, at step S806, the camera microcomputer 725 controls theimage pickup element drive circuit 723 so as to drive the image pickupelement 722 at a high-speed frame rate. In this situation, an imageprocessed by the image processing circuit 724 is displayed on thedisplay 726 at a high-speed frame rate. Subsequently, at step S807, thecontrast focus detection unit 730 performs the focus detection by thecontrast method at a high-speed frame rate. In this focus detection, thecamera microcomputer 725 performs a scanning operation in which thefocus lens is moved while obtaining contrast evaluation values. Asdescribed above, a start position of the scanning operation isdetermined based on the position determined, before the frame rateswitching, to be located near the in-focus position. The focus lens ismoved to a position at which the contrast evaluation value reaches apeak based on a result of the scanning, and then the AF processing iscompleted.

As described above, the camera microcomputer 725 determines whether ornot the focus lens is located at the near in-focus position when it isto perform the focus control. When the camera microcomputer 725determines that the focus lens is located at the near in-focus position,it moves the focus lens from the near in-focus position while switchingthe frame rate of the image pickup element 722 from the low-speed framerate to the high-speed frame rate. When for example the contrastevaluation value is higher than a predetermined threshold value, thecamera microcomputer 725 determines that the focus lens is located atthe near in-focus position.

According to the flowchart of FIG. 14, at the beginning of the focusdetection, the camera microcomputer 725 starts driving the focus lenswithout using a focus evaluation value obtained based on a contrastevaluation value. Then, the camera microcomputer 725 switches the framerate from the low-speed frame rate to the high-speed frame rate whiledriving the focus lens. This enables to perform a high-speed focusdetection control.

Other Embodiments

Embodiments of the present invention can also be realized by a computerof a system or apparatus that reads out and executes computer executableinstructions recorded on a storage medium (e.g., non-transitorycomputer-readable storage medium) to perform the functions of one ormore of the above-described embodiment(s) of the present invention, andby a method performed by the computer of the system or apparatus by, forexample, reading out and executing the computer executable instructionsfrom the storage medium to perform the functions of one or more of theabove-described embodiments. The computer may comprise one or more of acentral processing unit (CPU), micro processing unit (MPU), or othercircuitry, and may include a network of separate computers or separatecomputer processors. The computer executable instructions may beprovided to the computer, for example, from a network or the storagemedium. The storage medium may include, for example, one or more of ahard disk, a random-access memory (RAM), a read only memory (ROM), astorage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™)a flash memory device, a memory card, and the like.

The first and second embodiments can provide an image pickup apparatuscapable of performing high-speed shooting with suppressed consumptioncurrent and temperature rise, a method of controlling the image pickupapparatus, and a non-transitory computer-readable storage medium. Thethird and fourth embodiments can provide an image pickup apparatuscapable of displaying a desired live view while performing high-speedfocus detection, a method of controlling the image pickup apparatus, anda non-transitory computer-readable storage medium.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2013-131460, filed on Jun. 24, 2013, Japanese Patent Application No.2013-096472, filed on May 1, 2013, and Japanese Patent Application No.2014-035372, filed on Feb. 26, 2014, which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. An image pickup apparatus comprising: an imagepickup element configured to photoelectrically convert an optical image;a first detection unit configured to perform focus detection by using afocus signal generated from a high frequency component of an imagesignal outputted from the image pickup element; a second detection unitconfigured to perform focus detection by a method different from thefocus detection by the first detection unit; and a controller configuredto control a drive of a focus lens and configured to control a framerate, wherein when a predetermined operation to instruct focusing isperformed, the controller is configured to switch the frame rate from afirst frame rate to a second frame rate, which is faster than the firstframe rate, and perform a first operation to drive the focus lens forthe focus detection by the first detection unit, wherein the controlleris configured to start driving the focus lens based on a focus detectionresult by the second detection unit before completion of switching theframe rate from the first frame rate to the second frame rate.
 2. Theimage pickup apparatus according to claim 1, wherein the seconddetection unit is configured to perform the focus detection by a phasedifference method.
 3. The image pickup apparatus according to claim 2,wherein the image pickup element is configured to generate a pair ofimage signals for the focus detection by the phase difference method,and wherein the second detection unit is configured to perform the focusdetection by using the pair of image signals generated by the imagepickup element.
 4. The image pickup apparatus according to claim 3,wherein the second detection unit is configured to perform the focusdetection by using the pair of image signals generated by the imagepickup element at the first frame rate before the predeterminedoperation is performed.
 5. The image pickup apparatus according to claim1, wherein when a reliability of the focus detection by the seconddetection unit is determined to be high, the controller is configured tostart driving the focus lens based on the focus detection result by thesecond detection unit before completion of switching the frame rate fromthe first frame rate to the second frame rate.
 6. The image pickupapparatus according to claim 5, wherein when the reliability of thefocus detection by the second detection unit is not determined to behigh, the controller is configured not to start driving the focus lensbefore completion of switching the frame rate from the first frame rateto the second frame rate.
 7. The image pickup apparatus according toclaim 3, wherein when the pair of image signals generated by the imagepickup element is determined to be high, the controller is configured tostart driving the focus lens based on the focus detection result by thesecond detection unit before completion of switching the frame rate fromthe first frame rate to the second frame rate.
 8. The image pickupapparatus according to claim 3, wherein the image pickup element hasplural focus detection pixels configured to receive light beams whichpass through pupil regions of an image pickup optical system differentfrom each other.
 9. An image pickup apparatus comprising: an imagepickup element configured to photoelectrically convert an optical image;a detection unit configured to perform focus detection by using a focussignal generated from a high frequency component of an image signaloutputted from the image pickup element; and a controller configured tocontrol a drive of a focus lens and configured to control a frame rate,wherein when a predetermined operation to instruct focusing isperformed, the controller is configured to switch the frame rate from afirst frame rate to a second frame rate, which is faster than the firstframe rate, and perform a first operation to drive the focus lens forthe focus detection by the detection unit, wherein when the controllerdetermines that the focus lens is near an in-focus position, thecontroller is configured to start driving the focus lens to a startposition of the first operation before completion of switching the framerate from the first frame rate to the second frame rate.
 10. The imagepickup apparatus according to claim 9, wherein when the focus signal ishigher than a predetermined threshold, the controller is configured todetermine that the focus lens is near the in-focus position.
 11. Amethod of controlling an image pickup apparatus, the method comprisingthe steps of: converting photoelectrically an optical image in an imagepickup element; switching, when a predetermined operation to instructfocusing is performed, a frame rate from a first frame rate to a secondframe rate, which is faster than the first frame rate; performing afirst operation to drive a focus lens for focus detection by a firstdetection unit configured to perform the focus detection by using afocus signal generated from a high frequency component of an imagesignal outputted from the image pickup element; and wherein driving thefocus lens is started based on a focus detection result by a seconddetection unit configured to perform focus detection by a methoddifferent from the focus detection by the first detection unit beforecompletion of switching the frame rate from the first frame rate to thesecond frame rate.
 12. A method of controlling an image pickupapparatus, the method comprising the steps of: convertingphotoelectrically an optical image in an image pickup element;switching, when a predetermined operation to instruct focusing isperformed, a frame rate from a first frame rate to a second frame rate,which is faster than the first frame rate; and performing a firstoperation to drive a focus lens for a focus detection by a detectionunit configured to perform the focus detection by using a focus signalgenerated from a high frequency component of an image signal outputtedfrom the image pickup element, wherein when it is determined that afocus lens is near an in-focus position, driving the focus lens to astart position of the first operation is started before completion ofswitching the frame rate from the first frame rate to the second framerate.